· Max sessions —Save sessions are distributed based on each storage node device’s max sessions attribute. This is the default distribution method. the max sessions option is more likely to concentrate the backup load on fewer storage nodes, Max Sessions has a default values of 32 (FTD/AFTD) and 60 (DD Boost devices), which in most cases provides best performance. It cannot be set to a value greater than 60.
· Target sessions — Save sessions are distributed based on each storage node device’s target sessions attribute. This option is more likely to spread the backup load across multiple storage nodes.
Target Sessions is the number of sessions the device will handle before for another available device is used. For best performance, this should be set to a low value. The default values are 4 (FTD/AFTD) and 6 (DD Boost devices) and it may not be set to a value greater than 60.
· Max nsrmmd count is an advanced setting that can be used to increase data throughput by restricting the number of backup processes that the storage node can simultaneously run. When the target or max sessions are changed, the max nsrmmd count is automatically adjusted according to the formula MS/TS + 4. The default values are 12 (FTD/AFTD) and 14 (DD Boost devices).
o This feature is not available for clone and recover operations.
o The Target sessions attribute allows you to set the optimal number of backup sessions accepted by an active device. This is not a hard limit; to set a hard limit for the number of sessions to a particular device, use the Max sessions attribute.
o In the Max nsrmmd count field, specify the maximum number of nsrmmd processes that can run on the device. Use this setting to balance the nsrmmd load among devices. If Dynamic nsrmmds is enabled on the storage node, this value is automatically adjusted by the formula max/target +4, with the default value being 14. Otherwise, the default value is 4.
|Max sessions : NetWorker client save sessions are distributed among eligible storage nodes as follows:||Target sessions: NetWorker client save sessions are distributed among eligible storage nodes as follows:|
|Identify the available storage nodes in the NetWorker client’s Storage node affinity list.||Identify the available storage nodes in the NetWorker client’s Storage node affinity list.|
|Use an available device on the first storage node in the list that is working below its target sessions level.||Use an available device on the first storage node in the list that is working below its target sessions level.|
|When all devices on the first storage node are running at their target sessions level but some are running below their max sessions level, then use the least loaded device.||When all devices on the first storage node are running at their target sessions levels, continue to the next storage node even if some devices are running below their max sessions level.|
|When all devices on the first storage node are running at their max sessions level, continue to the next storage node and repeat the device selection process described previously in steps 2 and 3.||When all devices on all eligible storage nodes are running at their target sessions level, use the least loaded device that is running below its max session value.|
|Continue until all available devices on all storage nodes in the client’s storage node affinity list are in use||Continue with step 4 until all devices on all available storage nodes are running at their max session levels.|
Controls how many savestreams the server accepts at the same time. The more savestreams the server can accept, the faster the devices and clients’ disks run, up to the limit of their performance or the limits of the connections between them. Server Parallelism at a minimum should be equal to the sum of all of the target sessions for each defined device on the NetWorker server (included devices in remote storage nodes).
Sets the target number of savestreams to write to a device at the same time. Because this value is not a limit, a device might receive more sessions than the target sessions attribute specifies (can happen when server parallelism exceeds sum of all target sessions). The larger the number of sessions you specify for target sessions, the more save sets are multiplexed, or interleaved, onto the same volume.
Controls how many savestreams a client can send at the same time. Its value should be equal to the sum of the savesets for each client (that is, on a Windows 2000 client with the c:, d:, SYSTEM STATE and SYSTEM DB defined would have a client parallelism of 4.
Number of server parallelisms that can be allocated for that savegroup. This is useful if you have more than one savegroup running at the same time and would like one group to take more precedence than another. If value is greater than 0, it will override other parallelism settings the savegroup might use to avoid over utilizing the system’ resources.
Defined by using the Max parallelism attribute of the Pool resource, found in the NetWorker Console in the Media window, on the Configuration tab of the Pool property dialog box.
Pool parallelism determines the maximum number of simultaneous save streams for each device belonging to a NetWorker pool. The default value for this attribute is 0, which means that the attribute will have no effect on other parallelism settings.Pool parallelism can be used to increase recovery times.
Follow these guidelines to adjust the Parallelism and Target Sessions attributes for the best server performance:
- Set the server Parallelism and Target Sessions attributes so that the total of the performance of the disk drives equals the total performance of the tape drives. If you set the Parallelism attribute to a higher value, there is no benefit.
- To select the right values for the Parallelism and Target Sessions attributes, use the following equation:
Parallelism = Number of Devices * Target Sessions
For example, if you have three tape drives available for backup, and you want each tape drive to accept two savestreams, set the value of server parallelism to 6 and the value of target sessions to 2.
- When a NetWorker server is saving a large number of save sets, such as 500 or more, memory consumption and file descriptor consumption can reach values that are close to operating system limitations. In this event, the parallelism may need to be lowered.
- Decrease the server Parallelism and Target Sessions attributes to unload an overworked NetWorker server. With the correct settings, the normal operation of the computer should not be interrupted by backups or other NetWorker server activities.
- Add more memory to handle a higher parallelism setting.
Some tunable parameters in NetWorker:
- Client parallelism (limit simultaneous save steams per client)
- Server parallelism (Maximum Server limit for simultaneous save steams)
- Device target sessions/device maximum sessions (controlling save steam multiplexing to devices)
- Group Parallelism (limit simultaneous save steams per group)
Dynamic nsrmmd :The dynamic nsrmmd attribute in the NSR storage node attribute is off by default for the dynamic provisioning of nsrmmd processes. Turning on the dynamic nsrmmd attribute enables dynamic nsrmmd provisioning.
When the dynamic nsrmmd attribute is enabled and the number of sessions to a device exceeds the number of target sessions, the visible change in behavior is multiple nsrmmd processes on the same device. This continues until the max nsrmmd count, or max sessions values are reached, whichever is lower.